Magnetoresistive sensing element and magnetic head using the magnetoresistive sensing element

ABSTRACT

The present invention is intended to improve the linear response characteristics of resistance changes to the magnetic field. According to the present invention, an MR sensing element  10  comprises a sensing pattern  12  consisting of a magnetoresistive layer whose resistance changes in accordance with the direction of magnetization M, and an electrode layer for applying a sense current J to the sensing pattern  12.  The sensing pattern  12  is formed to be of circular shape. According to the present invention, since the demagnetic field within the sensing pattern is made constant with respect to the direction of the magnetization M, the improved linear response characteristics of resistance changes to an external magnetic field Hs can be realized.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetoresistive (to be referred toas MR hereinafter) element whose direct current resistance changes inaccordance with a magnetic field, and to a magnetic head using the MRelement.

2. Description of the Related Art

It is typically necessary for a magnetic disk apparatus to comprise amagnetic recording medium for recording magnetic information and amagnetic head for detecting a magnetic field generated from the magneticinformation in the magnetic recording medium. In the conventionalmagnetic head, a sensing electromagnetic inductive element for detectingthe magnetic field has been widely used. Such an electromagneticinductive type sensing element which is, however signals, low in theoutput voltage of reproducing magnetic recording, has beendisadvantageously unsuited for high-density recording.

To overcome the disadvantage, an MR type magnetic head using an MRsensing element was invented and has lately been put to practical use.

FIGS. 10 and 11 show a conventional MR sensing element. Specifically,FIG. 10 is a plan view showing the constitution of the conventional MRsensing element. FIG. 11 is a graph showing resistance vs. magneticfield transfer curve for magnetoresistance characteristics. Descriptionwill now be given to the prior art with reference to FIGS. 10 and 11.

A conventional MR sensing element 79 comprises a sensing pattern 80consisting of a magnetoresistive layer whose resistance changes inaccordance with the direction between magnetization M applied sensecurrent J to the sensing pattern 80. The sensing pattern 80 is made of,for example, an NiFe alloy thin layer and is of rectangular shape. Thesensing pattern 80 is constructed such that effective anisotropy isoriented parallel to the longer side of the rectangle and that in orderto provide the linear response characteristics of resistance changes toan external field Hs, a bias field is applied to the sensing pattern 80in advance and the magnetization M within the sensing pattern 80 therebyforms approximately 45° with the sense current J when Hs=0. On bothsides of the sensing pattern 80, domain stabilizing layers 82, 82 areprovided for making the magnetic domain structure of the sensing pattern80 a single domain.

When the external field Hs is applied, the magnetization M of thesensing pattern 80 rotates in accordance with the magnitude of Hs. Theresistance of the sensing pattern 80 then changes in accordance with anangle q of the magnetization M to the sense current J as shown in FIG.11. In case that the external field Hs is the magnetic field of a signalfrom a magnetic recording medium, a high sensitivity magnetic head canbe realized by electrically detecting resistance changes.

The conventional MR sensing element 79 has the sensing pattern 80 ofrectangular shape. In such a sensing pattern having sides with differentlengths, the demagnetic field within the pattern is not constant withrespect to the direction of the magnetization M. In order words, themagnitude of the demagnetic field is small in the long axis directionand large in the short axis direction. Due to this, as shown in FIG. 11,the magnetoresistance to the external field Hs show transfer curvehaving a flexion 84. Thus, the linear response charatceristics ofresistance changes to the magnetic field is disadvantageously low.

SUMMARY OF THE INVENTION

It is therefore the object of the present invention to provide an MRsensing element with the improved linear response characteristic ofresistance changes to the magnetic field, and a magnetic head using theMR sensing element.

The magnetoresistive sensing element according to the present inventioncomprises:

a sensing pattern consisting of a magnetoresistive layer whoseresistance changes in accordance with the direction of magnetization;and

an electrode layer for applying a sense current to the sensing pattern,wherein the sensing pattern is formed to be of substantially circularshape.

The magnetoresistive sensing element according to the present inventionfurther comprises a domain stabilizing layer for making the magneticdomain structure of the sensing pattern a single magnetic domain,wherein

the domain stabilizing layer is provided on each side of the sensingpattern and

the electrode layer is formed on the domain stabilizing layer.

This arrangement permits the demagnetic field within the sensing patternto be constant with respect to the magnetization direction and canthereby provide the improved linear response characteristics ofresistance changes to the external field.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features believed characteristic of the invention are setforth in the appended claims. The invention itself, however, as well asother features and advantages thereof, will be best understood byreference to the detailed description which follows, read in conjunctionwith the accompanying drawings, wherein:

FIG. 1 is a plan view showing the structure of an MR sensing element ofa first embodiment according to the present invention;

FIG. 2 is a graph showing the magnetoresistance transfer curve of the MRsensing element shown in FIG. 1;

FIG. 3 is a plan view showing the constitution of an MR sensing elementof a second embodiment according to the present invention;

FIG. 4 is an end view showing an MR sensing element of a thirdembodiment according to the present invention;

FIG. 5 is an end view showing an MR sensing element of a fourthembodiment according to the present invention;

FIG. 6 is a cross-sectional view showing an MR sensing element of afifth embodiment according to the present invention;

FIG. 7 is a cross-sectional view showing an MR sensing element of asixth embodiment according to the present invention;

FIG. 8 is a cross-sectional view showing the constitution of a magnetichead of the first embodiment according to the present invention;

FIG. 9 is a cross-sectional view showing the constitution of a magnetichead of the second embodiment according to the present invention;

FIG. 10 is a plan view showing the constitution of the conventional MRsensing element; and

FIG. 11 is a graph showing the magnetoresistance charatceristics of theconventional MR sensing element shown in FIG. 10.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 and 2 show an MR sensing element of a first embodiment accordingto the present invention. Specifically, FIG. 1 is a plan view showingthe constitution of the MR sensing element. FIG. 2 is a graph showingmagnetoresistance characteristics. Description will be given to thefirst embodiment with reference to FIGS. 1 and 2.

In this embodiment, an MR sensing element 10 comprises a sensing pattern12 consisting of a magnetoresistive layer whose resistance changes inaccordance with the direction between magnetization M and applied sensecurrent J to the sensing pattern 12. The sensing pattern 12 is formed tobe of circular shape.

The sensing pattern 12 is manufactured by, for example, the followingsteps. An NiFe layer having a thickness of 20 nm is deposited on asubstrate by a sputtering technique. The NiFe layer is processed to beof circular shape by a photolithography technique. The sensing pattern12 is ion-milled to a circle having a diameter of 6 μm at a chord 16having a length Tw=2 μm. The surface perpendicular to a surfaceincluding the chord 16 is ABS surface.

On both sides of the sensing pattern 12, domain stabilizing layers 14,14 are provided for making the magnetic domain structure of the sensingpattern 12 a single magnetic domain. The domain stabilizing layer 14consists of an NiFe thin layer having laminated anti-ferromagneticlayers sucb as NiMn or NiO layers. The anisotropic direction of thedomain stabilizing layer 14 is parallel to the direction of the sensecurrent J and the direction of magnetization Ms of the domainstabilizing layer 14 is the same as that of the sense current J.

The function of the MR sensing element 10 will now be described. Themagnetization M of the sensing pattern 12 is oriented at approximately45° to the sense current J by a bias field (not shown). When an externalfield Hs is applied, the magnetization M of the sensing pattern 12rotates from the stable direction. Since the sending pattern 12 iscircular, the magnitude of a demagnetizing field is almost constant asthe rotation angle of the magnetization M changes. As a result, as shownin FIG. 2, the change rate of resistance of the sensing pattern 12 issubstantially constant irrespectively of the direction of the externalfield Hs. Thus, the good linear response characteristics of theresistance of the sensing pattern 12 to the magnetic filed is obtained.

FIG. 3 is a plan view showing an MR sensing element of a secondembodiment according to the present invention. Description will be givento the second embodiment with reference to FIG. 3.

In this embodiment, an MR sensing element 20 comprises a sensing pattern22 consisting of a magnetoresistive layer whose resistance changes inaccordance with the direction of magnetization M. The sensing pattern 22is formed to be of circular shape. On both sides of the sensing pattern22, domain stabilizing layers 24, 24 are provided for making themagnetic domain structure of the sensing pattern 22 a single domainstructure. The MR sensing element 20 of this embodiment is the same asthe MR sensing element 10 of the first embodiment except that the lengthof a chord 26 is longer than that of the chord 16 to Tw=2.5 μm. Thechord 26 is a section at which an external field Hs is effectivelydetected. In a magnetic head using the MR sensing element 20, the chord26 serves as a parameter for determining a trackwidth which is almostequal to the length Tw. Thus, the length of the chord 26 can be changedin accordance with, for example, a trackwidth.

FIG. 4 is an end view showing the constitution of an MR sensing elementof a third embodiment according to the present invention. Descriptionwill be given to the third embodiment with reference to FIG. 4.

In this embodiment, an MR sensing element 30 comprises a sensing pattern32 consisting of a magnetoresistive layer whose resistance changes inaccordance with the direction of magnetization M, and an electrode layer34 for applying a sense current J to the sensing pattern 32. The sensingpattern 32 extends in a direction perpendicular to FIG. 4 and is formedto be of circular shape. On both sides of the sensing pattern 32, domainstabilizing layers 36, 36 are provided for making the magnetic domainstructure a single domain. The

The domain stabilizing layer 36 is a permanent magnetic thin layer madeof a permanent magnetic material. The permanent magnetic thin layerconsists of a CoCrPt alloy layer having a thickness of about 15 nm andis provided on a substrate 38 by a sputtering technique. The permanentmagnetic thin layer has a coercive force Hc of 500 to 1000 Oe. Thereason the coercive force is set Hc>500 Oe is that it is necessary forthe coercive force of the permanent magnetic thin layer to be madesufficiently greater than that of the magnetic field of an externalsignal, which is typically about 100 Oe. The electrode layer 34 is ametal layer having a thickness of 300 nm and is provided on the domainstabilizing layer 36 by a sputtering technique. The remaining conditionsis the same as that in the first embodiment described before.

FIG. 5 is an end view showing the constitution of an MR sensing elementof a fourth embodiment according to the present invention. Descriptionwill be given to the fourth embodiment with reference to FIG. 5.Elements having the same reference numerals as those in FIG. 4 will notbe described here.

In this embodiment, an MR sensing element 40 comprises a sensing pattern44 consisting of magnetoresistive layer 42 whose resistance changes inaccordance with the direction of magnetization M. On both sides of thesensing pattern 44, domain stabilizing layers 36, 36 are provided formaking the magnetic domain structure of the sensing pattern 44 a singlemagnetic domain. The sensing pattern 44 extends in a directionperpendicular to the view of FIG. 5 and is formed to be of circularshape, depending on the shape of the domain stabilizing layer 36.

The magnetoresistive layer 42 is an NiFe alloy thin layer and iscontinuously provided on a substrate 38 while contacting with the domainstabilizing layer 36. The domain stabilizing layer 36 is ananti-ferromagnetic NiMn layer and is formed to have a thickness of 30 nmby a sputtering technique. The uni-anisotropic direction of the layer 36is parallel to that of the sense current J. Since the exchange field isgenerated at the interface between the domain stabilizing layer 36 andthe magnetoresistive layer 42, the magnetization of the magnetoresistivelayer 42 is fixed to the uni-anisotropic direction of the domainstabilizing layer 36. Due to this, an effective magnetic field isgenerated in the MR sensing element 40 in this direction, to therebymake the magnetic domain structure of the magnetoresistive layer 42 asingle magnetic domain. The same advantage can be obtained if the domainstabilizing layer 36 is formed of a ferrimagnetic thin layer such as aGdFe layer.

FIG. 6 is a cross-sectional view showing the constitution of an MRsensing element of a fifth embodiment according to the presentinvention. Description will be given to the fifth embodiment withreference to FIG. 6.

In this embodiment, a sensing pattern 50 is of three-layer structureconsisting of an MR thin layer 501, a nonmagnetic layer 502 and a biasfield application layer 503. The bias field application layer 503 is asoft magnetic sputtered layer such as CiZrMo layer. The layer 503 isprovided for obtaining the linear response characteristic of the sensingelement to the magnetic field. The MR thin layer 501 serving as asensing section is an NiFe sputtered layer having a thickness of 20 nm.The MR thin layer 501 is provided on the bias field application layer503 through the nonmagnetic layer 502 of a Ti thin layer having athickness of 5 nm so as to orient the magnetization M at 45° to thelongitudinal direction of the layer. The remaining constitution is thesame as that described in the embodiments 1 through 5.

FIG. 7 is a cross-sectional view showing the structure of an MR sensingelement of a sixth embodiment according to the present invention.Description will be given to the sixth embodiment with reference to FIG.7.

In this embodiment, a sensing pattern 52 is of a four-layer structureconsisting of a magnetization rotating layer 521, a nonmagneticconductive layer 522, a fixed magnetization layer 523 and amagnetization fixing layer 524. This structure is a so-called spin valvestructure. The magnetization fixing layer 524 consists of an NiMnanti-ferromagnetic layer. The fixed magnetization layer 523 consists ofa Co layer for generating fixed magnetization. The nonmagneticconductive layer 522 consists of a Cu thin layer. The magnetizationrotating layer 521 consists of a soft magnetic NiFe thin layer in whicha magnetic field freely rotates in accordance with the magnetic field ofa recorded signal. The remaining structure is the same as that describedin the embodiments 1 through 5.

FIG. 8 is a cross-sectional view showing a layer structure of a magnetichead of the first embodiment according to the present invention.Description thereto will be given with reference to FIG. 8. Elementshaving the same reference numerals as those in FIG. 4 will not bedescribed here.

As shown in FIG. 8, a magnetic head 60 has a structure that an MRsensing element 30 is put between soft magnetic layers 62 and 64 throughnonmagnetic insulating layers 66 and 68 in order to improve thereproduction resolution of signal information. The soft magnetic layers62 and 64 are magnetic shields each consisting of an NiFe thin layerhaving a thickness of 2 μm. The nonmangetic insulating layers 66 and 68are gap layers. According to the magnetic head 60, when the nonmagneticinsulating layers 66 and 68 have a thickness of 100 nm, reproducedpattern density shows a resolution of not less than 130 kb per inch.

FIG. 9 is a cross-sectional view showing a layer structure of a magnetichead of the second embodiment according to the present invention.Description thereto will be given with reference to FIG. 9. Elementshaving the same reference numerals as those in FIG. 4 will not bedescribed here.

As shown in FIG. 9, a magnetic head 70 has a structure that an MRsensing element 30 is put between soft magnetic layers 72 and 74,serving as part of a yoke, through nonmagnetic insulating layers 76 and78. The magnetic head 70 is a yoke-type magnetoresistance magnetic head.The head 70 is provided with a nonmagnetic insulating layer 701, a coilconductive layer 702, a soft magnetic layer 703, a write gap 704 and thelike. According to the magnetic head 70, even if the head 70 and amagnetic recording medium move slidably to each other, the slidingportion of the head 70 is the write gap 704 and the MR sensing element30 comes in no direct contact with the magnetic recording medium, thusmaking it possible to reduce resultant noise to the minimum.

The MR sensing element according to the present invention has a sensingelement formed to be of circular shape. Due to this, the demagneticfield within the sensing pattern can be made almost constant withrespect to the direction of magnetization and the linear responsecharacteristics of resistance changes to the magnetic field can bethereby improved. Moreover, the magnetic head according to the presentinvention uses the MR sensing element according to the presentinvention. Due to this, the improved symmetric property of reproducedwaveforms can be obtained and a highly reliable magnetic recordingapparatus can be thereby realized.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications of the illustrative embodiments,as well as other embodiments of the invention, will be apparent topersons skilled in the art upon reference to this description. It is,therefore, contemplated that the appended claims will cover any suchmodifications or embodiments as fall within the true scope of theinvention.

What is claimed is:
 1. A magnetoresistive sensing element comprising: asensing pattern consisting of a magnetoresistive layer whose resistancechanges in accordance with a direction of magnetization; and anelectrode layer for applying a sense current to said sensing pattern,wherein said sensing pattern is formed to be of substantially circularshape.
 2. The magnetoresistive sensing element according to claim 1,further comprising a domain stabilizing layer for making a magneticdomain structure of said sensing pattern a single magnetic domain,wherein said domain stabilizing layer is provided on each side of saidsensing pattern, and said electrode layer is provided on said domainstabilizing layer.
 3. The magnetoresistive sensing element according toclaim 2, wherein said domain stabilizing layer comprises at least one ofan anti-ferromagnetic layer and a ferrimagnetic layer.
 4. Themagnetoresistive sensing element according to claim 2, wherein saiddomain stabilizing layer comprises at least one of NiMn, NiO and GdFe.5. The magnetoresistive sensing element according to claim 2, whereinsaid domain stabilizing layer is a permanent magnetic thin layer made ofa permanent magnetic material.
 6. The magnetoresistive sensing elementaccording to claim 5, wherein said permanent magnetic material is aCoCrPt alloy layer.
 7. The magnetoresistive sensing element according toclaim 5, wherein said permanent magnetic thin layer has a coercive forceof not less than 500 Oe.
 8. The magnetoresistive sensing elementaccording to claim 1 or 2, wherein said sensing pattern is of a laminatestructure consisting of a soft magnetic layer, a nonmagnetic layer and amagnetoresistive layer in due order.
 9. The magnetoresistive sensingelement according to claim 1 or 2, wherein said sensing pattern is of alaminate structure consisting of a magnetization fixing layer, a fixedmagnetization layer, a nonmagnetic conductive layer and a soft magneticlayer in due order.
 10. A magnetic head comprising: a first softmagnetic layer; a second soft magnetic layer; a nonmagnetic insulatinglayer; and a magnetoresistive sensing element according to claim 1 or 2put between said first and second soft magnetic layers through saidnonmagnetic insulating layer.